Conventionally, an audio communication system for transmitting a voice signal from a transmission terminal to a reception terminal via a communication line is provided. However, the partial or entire voice signal may become defective in a communication path between the transmission terminal and the reception terminal and a voice from the transmission terminal may be interrupted in the reception terminal, according to a communication situation.
As an example of a system for notifying a user of an error of communication between the transmission terminal and the reception terminal, a system described in Patent Literature 1 is known. A mobile communication system including a mobile communication terminal measuring an ambient field strength and a remaining battery capacity and transmitting the measured field strength and remaining battery capacity to a base station and the base station determining whether communication is disconnected due to a decrease in the field strength or a decrease in the remaining battery capacity of the mobile communication terminal by referring to a measurement result and notifying the mobile communication terminal of a determination result, when the communication is disconnected abruptly, is described in Patent Literature 1. In the mobile communication system, when the communication disconnection occurs, a message showing whether a cause of the error thereof is the field strength, the remaining battery capacity, or other abnormality is transmitted to the terminal, so that the cause of the communication disconnection can be recognized by a user of the mobile communication terminal.